JP6793574B2 - Low thermal expansion alloy - Google Patents

Description

The present invention relates to a low thermal expansion alloy, and more particularly to a low thermal expansion alloy having excellent hot workability, measures against casting cracks, and excellent machinability.

Thermally stable Invar alloys are widely used as component materials for electronics, semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment.

Since the Invar alloy is an Fe-high Ni alloy and solidifies as an austenite single phase, the segregation of impurity elements is large and coarse columnar crystals are likely to be formed. For this reason, cracks in the cast steel product, casting cracks in the ingot, and hot forging cracks in the forged steel product ingot are likely to occur.

Patent Document 1 discloses an Fe—Ni alloy showing a low coefficient of thermal expansion of 1.0 × 10 ^-6 / ° C. or less at a shadow mask operating temperature. The Fe-Ni alloy of Patent Document 1 has Ni + Co: 35.0 to 37.0% by weight, Co: 1.00% by weight or less, S: 0.005% by weight or less, B: 0.0005 to 0.0040% by weight. C: 0.01% by weight or less, Si: 0, respectively, containing at least one of C, Si, Mn, and Al added as a deoxidizing agent, which contains% and has a substantially Fe composition in the balance. The total content of .04% by weight or less, Mn: 0.14% by weight or less, Al: 0.003% by weight or less and C + Si + Mn + Al is regulated to 0.030 to 0.140% by weight, and 30 to 100 ° C. The coefficient of thermal expansion of is 1.0 × 10 ^-6 / ° C. or less.

Patent Document 2 discloses an Invar alloy having high strength, excellent hot workability, low manufacturing cost, and a low coefficient of thermal expansion below room temperature. The Invar alloy of Patent Document 2 has C: 0.015 to 0.10%, Si: 0.35% or less, Mn: 1.0% or less, P: 0.015% or less, S: 0 by weight ratio. .0010% or less, Cr: 0.3% or less, Ni: 35-37%, Mo: 0 to 0.5%, V: 0 to 0.05%, Al: 0.01% or less, Nb: 0. It contains 15% or more and less than 1.0%, Ti: 0.003% or less, N: 0.005% or less, B: 0.0005 to 0.005%, and the balance is composed of Fe and unavoidable impurities. It is a feature.

Patent Document 3 discloses an Fe—Ni alloy having excellent hot workability. The Fe-Ni alloy of Patent Document 3 has Ni: 30 to 80%, C: 0.03% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.03% or less by weight. , S: 0.03% or less, Cr: 7.0% or less, Al: 0.10% or less, and is an alloy composed of the balance Fe and unavoidable impurities, B: 0.001 to 0.03. It is characterized by containing%.

Japanese Unexamined Patent Publication No. 2000-129399 Japanese Unexamined Patent Publication No. 10-17997 Japanese Unexamined Patent Publication No. 60-159157

The coefficient of thermal expansion and hot workability of the Invar alloy disclosed in the above patent documents are not yet sufficient for recent demands. Further, as described above, the Invar alloy has a problem that cracks in the cast steel product, casting cracks in the ingot, and hot forging cracks in the forged steel product ingot are likely to occur.

An object of the present invention is to provide a low thermal expansion alloy having a further low coefficient of thermal expansion at room temperature, excellent hot workability, measures against casting cracks, and excellent machinability.

The present inventors have diligently studied a method for obtaining a low thermal expansion alloy having a low coefficient of thermal expansion, excellent hot workability, measures against casting cracks, and excellent machinability. As a result, by setting the component composition to which B is added in an appropriate range and performing solution treatment, it has a low coefficient of thermal expansion, excellent hot workability, countermeasures against casting cracks, and machinability. It was found that an excellent low thermal expansion alloy can be obtained.

The present invention has been made based on the above findings, and the gist thereof is as follows.

C: 0.04% or less, Si: more than 0.15%, 0.5% or less, Mn: 0.5% or less, S: 0.050% or less, Ni: 31-36%, Co: 2-6 5.5%, Al: more than 0.03%, 0.20% or less, Mg: 0 to 0.05%, Ca: 0 to 0.02%, Ce: 0 to 0.05%, La: 0 to 0 It contains 0.05%, Ti: 0 to 0.05%, B: 0.001 to 0.020%, and N: 0.0050% or less, and the balance is Fe and unavoidable impurities at 25 to 100 ° C. A low thermal expansion alloy characterized in that the average coefficient of thermal expansion of is 1.0 × 10 ^-6 / ° C. or less, and the drawing measured by a tensile test at 900 ° C. is 50% or more.

According to the present invention, a low thermal expansion alloy having a low coefficient of thermal expansion, excellent hot workability, measures against casting cracks, and excellent machinability can be obtained, so that it is thermally stable and high. It can be applied to the material of parts where strength is desired and cutting is required.

Hereinafter, the present invention will be described in detail. Hereinafter, "%" regarding the component composition shall represent "mass%" unless otherwise specified. First, the component composition of the casting of the present invention will be described.

C dissolves in austenite and contributes to an increase in strength. As the C content increases, the coefficient of thermal expansion increases. Further, the ductility is lowered, casting cracks are likely to occur, and the machinability is also lowered. Therefore, the content is set to 0.04% or less, preferably 0.02% or less. In the low thermal expansion alloy of the present invention, C is not an essential element and the content may be 0.

Si is added as a deoxidizing material. Furthermore, it adheres to the tool surface during cutting to form an oxide film, which suppresses seizure of the tool. Therefore, the amount of Si is set to more than 0.15%. If the amount of Si exceeds 0.5%, the coefficient of thermal expansion increases and the machinability also decreases. Therefore, the amount of Si is set to 0.5% or less, preferably 0.4% or less.

Mn is added as a deoxidizing material. It also contributes to the improvement of strength by strengthening the solid solution. Furthermore, it is also an element that combines with S to generate MnS and improves machinability. In order to obtain this effect, the amount of Mn is preferably 0.1% or more. Even if the Mn content exceeds 0.5%, the effect is saturated and the cost is high. Therefore, the Mn content is set to 0.5% or less, preferably 0.3% or less. Mn is not an essential element and its content may be zero.

S is an element that binds to Mn to generate MnS and improve machinability, and is preferably contained in an amount of 0.010% or more. However, if a large amount of S is contained, the hot workability is deteriorated and casting cracks are likely to occur. Therefore, the S content is set to 0.050% or less. S is also contained as an impurity, and even if it is not intentionally contained, it is contained in a certain amount, so that the content is usually more than 0.

Ni is an essential element that lowers the coefficient of thermal expansion. If the amount of Ni is too large or too small, the coefficient of thermal expansion will not be sufficiently small. In order to sufficiently reduce the coefficient of thermal expansion, the amount of Ni is set in the range of 31 to 36%, preferably 32 to 34%.

Co contributes to a decrease in the coefficient of thermal expansion when combined with Ni. In order to obtain a desired coefficient of thermal expansion, the range of Co is 2 to 6.5%, preferably 3.0 to 6.0%.

Al is added for the purpose of deoxidation. Further, by forming AlN, it is an element necessary for suppressing B from becoming BN and segregating B as a solid solution B at the grain boundary. In order to obtain this effect, the Al content is set to more than 0.03%. Further, in order to suppress the formation of inclusions, reduce casting defects, and obtain a lower coefficient of thermal expansion, the content is set to 0.20% or less, preferably 0.10% or less.

Mg has a function of suppressing grain boundary segregation of S by binding with S contained as an impurity and improving hot ductility. Further, Mg oxide or Mg vapor also has an effect as an inoculum. If the Mg content exceeds 0.05%, the viscosity of the molten metal is increased and casting defects may occur. Therefore, the Mg content is set to 0 to 0.05% or less. Mg is not an essential element and its content may be zero.

Ca combines with S to form sulfide, which is useful for improving hot workability and ductility at room temperature. If the Ca content exceeds 0.02%, the melting point of the alloy is lowered, and conversely, the hot workability is lowered. Therefore, the Ca content is set to 0 to 0.02% or less. Ca is not an essential element and its content may be zero.

Ce and La are elements that suppress the decrease in toughness due to sulfide. Since the effect is saturated when the contents of Ce and La exceed 0.05%, the contents of Ce and La are set to 0 to 0.05% or less, respectively. Ce and La are not essential elements, and the content may be 0.

Ti is added as an inoculum to produce solidified nuclei. Furthermore, by forming TiN, B is suppressed from becoming BN, and since B has a function of segregating B as a solid solution B at the grain boundary, fine equiaxed crystals are formed using these carbides and nitrides as solidification nuclei. It becomes easy to be done. In addition, these elements are also elements that improve hardness and tensile strength. As the content of Ti increases, the toughness deteriorates remarkably, so the content is set to 0 to 0.05% or less. Ti is not an essential element and its content may be zero.

B is an important element that has the effect of improving hot workability and preventing casting cracks by segregating as a solid solution B at the grain boundaries. In order to obtain this effect and further obtain good toughness, the content of B is 0.001 to 0.020%, preferably 0.002 to 0.010%. Further, it is preferable that 50% or more of the contained B is a solid solution B.

N is contained as an impurity. When a large amount of N is contained, B forms BN and the amount of solid solution B decreases. Therefore, the content of N needs to be limited to 0.0050% or less.

The rest of the composition is Fe and unavoidable impurities. The unavoidable impurities refer to those that are unavoidably mixed from the raw materials, the manufacturing environment, etc. when the steel having the component composition specified in the present invention is industrially manufactured. Specifically, P, O and the like of 0.02% or less can be mentioned.

By producing an alloy having the above chemical components by casting, it is possible to obtain a low thermal expansion alloy having excellent hot workability and further taking measures against casting cracks. The mold used for producing the low thermal expansion alloy of the present invention, the apparatus for injecting molten steel into the mold, and the injection method are not particularly limited, and known apparatus and methods may be used. Steel parts can be obtained by directly processing the produced cast alloy by cutting or the like, or by processing after forging.

The excellent hot workability of the low thermal expansion alloy of the present invention can be evaluated by the result of a tensile test (greeble test) at 900 ° C. Specifically, the low thermal expansion alloy of the present invention has a property of 50% or more, preferably 60% or more, more preferably 70% or more in drawing measured by a tensile test at 900 ° C.

Further, the low thermal expansion alloy of the present invention has excellent machinability. This effect can be confirmed by a turning test.

Further, in order to lower the coefficient of thermal expansion, solution treatment may be performed. The solution treatment is performed before processing or after casting and forging. In the solution treatment, the alloy is preferably heated to 650 to 850 ° C., preferably 600 to 1000 ° C., held for 0.5 to 5 hr, and then rapidly cooled. The cooling rate is preferably 10 ° C./min or higher, more preferably 100 ° C./min or higher. Due to the solution formation, the precipitates precipitated during casting are solid-solved, and the ductility and toughness are improved.

The low thermal expansion alloy having the component composition of the present invention can obtain a low coefficient of thermal expansion in which the average coefficient of thermal expansion at 25 to 100 ° C. is 1.0 × 10 ^-6 / ° C. or less.

After the solution treatment, if necessary, a known heat treatment such as stress relief annealing, which is held at 300 to 350 ° C. for 1 to 5 hours and then air-cooled, may be performed.

A plurality of cast steel products (Y block and ingot) were produced by pouring molten metal adjusted to have the composition shown in Tables 1 and 2 into a mold.

Two samples were taken from the Y block and subjected to a tensile test at a strain rate of 0.07 to 0.08 s ^-1 at 900 ° C., and the average values were taken as the measured values of tensile strength and drawing. Similarly, a test piece for measuring the coefficient of thermal expansion was taken, held at 750 ° C. for 2 hours, solution-treated at an average cooling rate of 200 ° C./min, held at 350 ° C. for 5 hours, and then air-cooled for stress relief annealing. The average coefficient of thermal expansion at ~ 100 ° C. was measured.

Further, a Φ25 round bar subjected to the above heat treatment was prepared from the Y block, and the machinability was evaluated by a turning test using a lathe. A cemented carbide tool (P20) was used for the test, and the turning conditions were a cutting speed of 200 m / min, a cutting feed of 0.1 mm / rev, a cutting depth of 0.3 mm, and no lubrication. The lateral flank wear width of the tool was measured from the start of turning to the elapse of 2000 seconds, and the case where the wear width was 0.12 mm or less was regarded as acceptable (◯), and the case where it was not was evaluated as rejected (x).

In addition, after casting the ingot, hot forging is performed with a forging molding ratio of 15, and the forging property is evaluated based on the presence or absence of cracks. Those without cracks are marked with "○" and those with cracks are marked with "x". did. From the forged steel product obtained by forging, a test piece for measuring the coefficient of thermal expansion was taken, held at 750 ° C for 2 hr, solution treatment with an average cooling rate of 200 ° C / min, and further held at 350 ° C for 5 hr, and then air-cooled stress. It was subjected to removal annealing, the average coefficient of thermal expansion at 25 to 100 ° C. was measured, and the above-mentioned machinability test was further performed. The results are shown in Tables 1 and 2.

The low thermal expansion alloy of the present invention has a low coefficient of thermal expansion and also shows a high drawing in a tensile test at 900 ° C. It also showed good machinability.

On the other hand, in the comparative example, the target characteristics could not be obtained with at least one of forgeability, machinability, and coefficient of thermal expansion.

Claims (1)

By mass%
C: 0.04% or less,
Si: Over 0.15%, 0.5% or less,
Mn: 0.5% or less,
S: 0.050% or less,
Ni: 31-36%,
Co: 2 to 6.5%,
Al: Over 0.03%, 0.20% or less,
Mg: 0-0.05%,
Ca: 0-0.02%,
Ce: 0-0.05%,
La: 0-0.05%,
Ti: 0-0.05%,
B: 0.001 to 0.020% and N: 0.0050% or less, and the balance is Fe and unavoidable impurities.
The average coefficient of thermal expansion at 25-100 ° C is 1.0 × 10 ^-6 / ° C or less.
A low thermal expansion alloy characterized in that the drawing measured in a tensile test at 900 ° C. is 50% or more.